In the manufacture of magnetic disk drive data storage devices, the magnetic disk drives incorporate one or more magnetic data storage disks. Each magnetic data storage disk typically is made of a thin flat glass disk with its planar surfaces closely controlled to be flat and parallel to each other. The surfaces of the data storage disks are coated with a layer of magnetically alterable material which will accept and maintain different magnetic orientations within very small domains. The magnetic data storage disks are incorporated into and rotated at a very high speed by the magnetic disk drive. The magnetic disk drive also incorporates at least one magnetic read/write head positionable adjacent the data recording surface. As the data recording disk rotates, the air flow proximate the data recording surface of the disk causes the read/write head to "fly" or levitate a very small distance above the magnetic data storage disk surface. The read/write head does not make contact with the recording surface during normal operations due to the flow of the air between the disk surface and the read/write head. The closer the read/write head can fly to the surface of the data disk without impacting or contacting the surface at the disk, the more densely the data may be recorded, thereby both increasing the data storage capacity of the magnetic storage disks and shortening the requisite read/write cycles to either retrieve or record the data.
In order to accommodate a very close read/write head flight height, it is necessary to present a very flat and very smooth data disk surface to the read/write head. The basis for a flat and smooth recording surface is a very flat and very smooth substrate surface. A flat and smooth surface of a glass disk substrate is created by polishing flat surfaces on a glass disk with polishing pads, typically hard pads of urethane incorporating therein particles of cerium. Cerium is a soft malleable metal which lends itself to high quality polishing. The cerium provides the abrasive needed both to accomplish the removal of the minute quantities of glass if used with a polishing fluid to produce the required, very smooth surface on the glass disk. A liquid containing a fine suspension of cerium particles is flooded between the surfaces being polished and a polishing pad to further abrade the glass disk surface and to carry away the minute glass particles removed during polishing from the glass disks. During the polishing of the disks, a conventional and well-known process, the urethane/cerium polishing pads become glazed with glass residue of the polishing process and small cerium particles that are eroded from the polishing pad. Any degradation of the surface of the polishing pads reduces the polishing efficiency of the polishing operation.
The cerium loaded urethane polishing pads are available fro Universal Photonics, Hicksville, N.Y. 11801. The preferred polishing pads are designated L66 Cerium Loaded Urethane Pads.
Therefore, dressing the polishing pads of a polishing machine is a normal but very time consuming maintenance requirement in a high quality polishing process to achieve the desired, high quality, polished surfaces. In order to renew the polishing surfaces of the polishing pad and remove the glazing and other debris from the surface of the polishing pad, a small portion of the surface of the polishing pad must be removed, abrading or cutting off and rendering exposed new surfaces of the cerium particles trapped in the urethane pad. The newly exposed surfaces of the cerium particles incorporated in the urethane matrix are abraded to a smooth surface.
Refer now to FIGS. 1, 2 and 3. Apparatus of the prior art as illustrated in FIG. 1 is a schematic of a portion of a conventional planetary polishing machine 10, as viewed from the top. Central rotary drive 12 is provided with a gear-shaped outer circumference 15 forming, in effect, a driven sun gear 14. Central rotary drive 12 is engaged by the outwardly projecting gear teeth 30 on the periphery of driven planetary ring 16. Planetary ring 16 is positioned intermediate the central rotary drive 12 and fixed interior ring gear 18, which is either formed into or positioned within the interior of tub 20. The tub 20 remains stationary; with gear teeth 30 on planetary ring 16 engaged with interior gear 18, the central rotary drive 12 rotates planetary ring 16, and thus, planetary ring 16 will be driven around the interior ring gear 18 within tub 20. Tub 20 supports a polishing pad 22 for polishing glass substrate disks (not shown) from which magnetic data storage disks are made.
The dressing rings 16 are annular rings 16 of a high strength metal such as steel or stainless steel, which support on each of their annular surfaces 26 a plurality of pellets 24, typically thirty to forty. These pellets 24, approximately 0.25 inches (6.4 mm) in height, 0.75 inch (19.1 mm) in diameter, are a matrix of material binding diamond particles 36. The pellets 24 are formed by sintering a hot isostatically pressed body of a mixture of nickel particles and diamond particles 36. The pellets 24 are bonded onto the metal ring 16. The metal rings 16 are provided with gear teeth 30 cut into the outer periphery 32 to mesh with the gear-shaped outer circumference 15 of central rotary drive 12. Dressing rings of the type described above may be secured from Mitsui Mining and Smelting Co., Osaka, Japan.
The planetary rings 16 are employed in sets; a plurality, preferably five, are used at one time in the polishing machine 10. Prior to the use of the dressing rings 16 in a dressing operation as well as at repeated intervals during the life of the dressing rings 16, the faces 34 of the pellets 24 are ground not only to be flat but also to be a uniform height above the ring surface 17. The surfaces 34 of the pellets 24 on opposite sides of rings 16 also must be ground completely parallel to each other to prevent one leading edge 28 of a pellet 24 from gouging the polishing pad 22.
The dressing of the polishing pads 22 is accomplished by lowering a similar polishing pad (not shown) onto the dressing rings 16 and particularly onto faces 34 of pellets 24 and rotating the central rotary drive 12. Because the pellets 24 move over the polishing pad 22, the sharp corners or leading edge 28 of the pellets 24 and the exposed edges of diamonds 36 cut and remove thin layers of urethane and cerium from the polishing pad 22, the smooth flat faces of the diamond particles smooth the surface of polishing pad 22. A fluid is flowed over the polishing pad 22 and dressing rings 16 to flush away dressed particles removed from the polishing pads 22. The fluid typically is water provided in a large enough flow to accomplish the desired flushing function.
To avoid damaging polishing pads 22 by concentrating excessive force on the interface between the polishing pad 22 and the nickel/diamond matrix pellets 24, polishing machine 10 is operated at a reduced speed and with only a moderate force exerted on the polishing pads 22 and on each dressing ring 16 by pellets 24.
The polishing machine 10 is operated in the dressing operation for a period of an hour or more, which is non-productive down time.